Planar light source

ABSTRACT

A planar light source includes a mounting substrate, a plurality of light sources, a partition member, a frame body, a wavelength conversion member, and a light diffusion plate. The light sources are arranged two-dimensionally on the mounting substrate in a plan view. The partition member includes a wall portion surrounding each of the light sources except for outermost ones of the light sources in the plan view. The wall portions are located inward of the outermost ones of the light sources. The frame body has a bottom portion and a lateral wall surrounding the mounting substrate. The wavelength conversion member is disposed on the lateral wall of the frame body. The light diffusion plate is disposed above the plurality of light sources and the wavelength conversion member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/331,479, filed on May 26, 2021. This applicationclaims priority to Japanese Patent Application No. 2020-95002 filed onMay 29, 2020, and Japanese Patent Application No. 2020-207548 filed onDec. 15, 2020. The entire disclosures of U.S. patent application Ser.No. 17/331,479 and Japanese Patent Application No. 2020-95002 andJapanese Patent Application No. 2020-207548 are hereby incorporatedherein by reference.

BACKGROUND Technical Field

The present disclosure relates to a planar light source and a liquidcrystal display device.

Background Art

Planar light sources using light emitting elements such as lightemitting diodes are widely used for various light sources such as abacklight for a liquid crystal display device and a display device.

An example of such a planar light source has a configuration includinglight emitting elements arranged two-dimensionally and a light diffusionplate disposed above the light emitting elements. For example, see JP2012-221779 A. In a planar light source described in JP 2012-221779 A,the light diffusion plate contains diffusion particles for diffusinglight emitted from light emitting portions of the light emittingelements. In this light diffusion plate, protrusions with a gentlecurved surface shape protruding toward the light emitting elements areintegrally formed at least in areas corresponding to the light emittingportions of the light emitting elements in a surface of the lightdiffusion plate proximate to the light emitting elements.

SUMMARY

An object of the present disclosure is to reduce unevenness inbrightness generated at a peripheral region of a planar light sourcehaving an irregular planar shape.

A planar light source according to an embodiment of the disclosureincludes a mounting substrate, a plurality of light sources, a partitionmember, a frame body, a wavelength conversion member, and a lightdiffusion plate. The light sources are arranged two-dimensionally on themounting substrate in a plan view. The partition member includes a wallportion surrounding each of the light sources except for outermost onesof the light sources in the plan view. The wall portions are locatedinward of the outermost ones of the light sources. The frame body has abottom portion and a lateral wall surrounding the mounting substrate.The wavelength conversion member is disposed on the lateral wall of theframe body. The light diffusion plate is disposed above the plurality oflight sources and the wavelength conversion member.

A planar light source according to an embodiment of the disclosureincludes a mounting substrate, a plurality of light sources, a framebody, a wavelength conversion member, and a light diffusion plate. Thelight sources are arranged two-dimensionally on the mounting substratein a plan view. The frame body has a bottom portion and a lateral wallsurrounding the mounting substrate. The wavelength conversion member isdisposed on the lateral wall of the frame body. A distance between thewavelength conversion member and an outermost light source among theplurality of light sources is greater than a distance between two lightsources among the plurality of light sources. The light diffusion plateis disposed above the plurality of light sources and the wavelengthconversion member.

According to one embodiment of the disclosure, unevenness in brightnessgenerated at a peripheral region can be reduced in a planar light sourcehaving an irregular planar shape.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic plan view illustrating a planar light sourceaccording to a first embodiment.

FIG. 2 is a schematic partially enlarged plan view of part B of FIG. 1 .

FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2 .

FIG. 4 is a schematic plan view illustrating the arrangement of thelight sources in the planar light source according to the firstembodiment.

FIG. 5 is a schematic plan view illustrating a light diffusion plate inthe planar light source according to the first embodiment.

FIG. 6 is a partially enlarged cross-sectional view of the vicinity ofthe light source of FIG. 3 .

FIG. 7 is a schematic plan view for describing a width of a thin plateportion (Part 1).

FIG. 8 is a schematic plan view for describing the width of the thinplate portion (Part 2).

FIG. 9 is a diagram showing a simulation result for a light diffusionplate (Part 1).

FIG. 10 is a diagram showing a simulation result for the light diffusionplate (Part 2).

FIG. 11 is a schematic cross-sectional view illustrating an arrangementof optical members.

FIG. 12 is a schematic partially enlarged cross-sectional viewillustrating a light diffusion plate of the planar light sourceaccording to a first modified example of the first embodiment (Part 1).

FIG. 13 is a schematic partially enlarged cross-sectional viewillustrating a light diffusion plate of the planar light sourceaccording to the first modified example of the first embodiment (Part2).

FIG. 14 is a schematic partially enlarged cross-sectional viewillustrating a light diffusion plate of the planar light sourceaccording to the first modified example of the first embodiment (Part3).

FIG. 15 is a schematic plan view illustrating the light diffusion plateof FIG. 14 .

FIG. 16 is a schematic partially enlarged plan view of a partitionmember according to a second modified example of the first embodiment.

FIG. 17 is a cross-sectional view taken along line B-B of FIG. 16 .

FIG. 18A is a schematic partially enlarged cross-sectional view in thevicinity of an outer edge of the planar light source (Part 1).

FIG. 18B is a schematic partially enlarged cross-sectional view in thevicinity of the outer edge of the planar light source (Part 2).

FIG. 19 is a schematic plan view explaining an outer shape of asubstrate in a planar light source according to a third modified exampleof the first embodiment.

FIG. 20 is a configuration diagram illustrating a liquid crystal displaydevice according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, certain embodiments of the present invention will bedescribed with reference to the drawings. In the description below,terms indicating a specific direction or position (e.g., “upper”,“lower”, and other terms including those terms) are used when necessary.The use of those terms is to facilitate understanding of the inventionwith reference to the drawings, and the technical scope of the inventionis not limited by the meaning of those terms. In addition, partsdesignated with the same reference numerals appearing in a plurality ofdrawings indicate identical or equivalent parts or members.

Further, the embodiments to be illustrated below exemplify planar lightsources for embodying the technical concept of the present invention,and do not limit the present invention to the description below. Inaddition, unless otherwise specified, the dimensions, materials, shapes,relative arrangements, and the like of constituent elements describedbelow are not intended to limit the scope of the present invention tothose, but are intended to be exemplified. Also, the contents describedin one embodiment can be applied to another embodiment and modifiedexamples. Further, the size, positional relationship, and the like ofthe members illustrated in the drawings can be exaggerated in order toclarify the explanation.

First Embodiment

Planar Light Source 10

FIG. 1 is a schematic plan view illustrating a planar light sourceaccording to a first embodiment. FIG. 2 is a schematic partiallyenlarged plan view of part E of FIG. 1 . FIG. 3 is a cross-sectionalview taken along line A-A of FIG. 2 . FIG. 4 is a schematic plan viewillustrating an arrangement of light sources in the planar light sourceaccording to the first embodiment, and is a view in which a partitionmember and a light diffusion plate in FIG. 1 are not illustrated. FIG. 5is a schematic plan view illustrating the light diffusion plate in theplanar light source according to the first embodiment. FIG. 6 is apartially enlarged cross-sectional view of the vicinity of the lightsource of FIG. 3 .

As illustrated in FIGS. 1 to 6 , a planar light source 10 is asurface-emitting light emitting device including a substrate 11, lightsources 12, a partition member 13, and a light diffusion plate 14. InFIGS. 1 and 2 , the structures under the light diffusion plate 14 (i.e.,the substrate 11, the light sources 12, and the partition member 13) areillustrated with solid lines in order to better show these structures.The partition member 13 is not an essential component of the planarlight source 10, but is provided when necessary. When the partitionmember 13 is not provided, for example, a supporting body that supportsthe light diffusion plate 14 can be provided.

In the description below, the term “in a plan view” refers to viewing atarget object in the normal direction to an upper surface 11 m of thesubstrate 11, and the term “planar shape” refers to the shape of thetarget object viewed in the normal direction to the upper surface 11 mof the substrate 11.

A plurality of light sources 12 each including a light emitting diodeare arranged on the substrate 11, which is a mounting substrate. Anyappropriate number of light sources 12 can be disposed on the substrate11.

The partition member 13 is disposed on the same side as the lightsources 12 of the substrate 11. The partition member 13 has a topportion 13 a disposed in a grid pattern in a plan view, and a wallportion 13 b surrounding each of the light sources 12 in a plan view,and includes a plurality of regions each surrounding a corresponding oneof the light sources 12. The wall portion 13 b of the partition member13, for example, extends from the top portion 13 a toward the substrate11. In a cross-sectional view, each space surrounded by correspondingportions of the wall portion 13 b that are opposite to each other has awidth reduced toward the substrate 11.

A region surrounded by corresponding portions of the wall portion 13 b(that is, the area and the space) is defined as a single section C, sothat the partition member 13 includes a plurality of sections C. In thepresent embodiment, a single light source 12 is disposed in a singlesection C. However, two or more light sources 12 can be disposed in asingle section C. In this case, for example, three light sources 12 ofred, green, and blue can be disposed in a single section C.Alternatively, two light sources 12 of a daylight color and a bulb colorcan be disposed in a single section C.

The light diffusion plate 14 is an optical member disposed on the topportion 13 a of the partition member 13 and disposed above the lightsource 12. With the light diffusion plate 14, the planar light source 10can have improved the uniformity of light. The light diffusion plate 14according to the present embodiment has a portion having a thinthickness on a peripheral region in order to reduce unevenness inbrightness on the peripheral region of the planar light source 10.

The outermost contour portion of each member in a plan view is referredto as an “outer edge”, and an area having a width and including theouter edge in a plan view is referred to as a peripheral region. Inparticular, the term “peripheral region of the light diffusion plate 14”refers to an area of the light diffusion plate 14 located outward ofperipheral light sources 12 (outermost light sources) of the pluralityof light sources 12 in a plan view. The peripheral region does notnecessarily represent an annular region.

Hereinafter, components constituting the planar light source 10 will bedescribed in detail.

Substrate 11

The substrate 11 is a member on which the plurality alight sources 12are arranged, and has an irregular shape. The term “irregular shape” asused herein refers to a shape other than a rectangular shape, such as anon-rectangular shape partially or entirely modified from a perfectrectangular shape in order to correspond to a predetermined productshape.

As illustrated in FIG. 6 , conductor wirings 18A and 18B for supplyingelectric power to the light sources 12 such as the light emittingelements 12 a are disposed on the upper surface 11 m of the substrate11. Portions of the conductor wirings 18A and 18B that are not to beelectrically connected to the light emitting elements 12 a arepreferably covered with a covering member 15.

The material of the substrate 11 can be any appropriate material thatcan insulate at least between a pair of conductor wirings 18A and 18B,and examples thereof include ceramics, resins, and composite materials.Examples of the ceramics include alumina, mullite, forsterite, glassceramics, nitride-based ceramics (e.g., AlN), carbide-based ceramics(e.g, SiC), and LTCC. Examples of the resin include phenol resin, epoxyresin, polyimide resin, BT resin, polyphthalamide (PPA), andpolyethylene terephthalate (PET), Examples of the composite materialinclude the resins described. above with an inorganic filler such asglass fiber, SiO₂, TiO₂, or Al₂O₃ mixed in the resins, a glass fiberreinforced resin (glass epoxy resin), and a metal substrate having aninsulating layer formed on the metal member.

The thickness of the substrate 11 can be appropriately selected. Thesubstrate 11 can be either a flexible substrate that can be manufacturedin roll-to-roll processing or a rigid substrate. The rigid substrate canbe a bendable thin rigid substrate. For the conductor wirings 18A and18B, any appropriate material can be used as long as it is a conductivemember, and a material commonly used for a wiring layer of a circuitboard or the like can be used. A plating film, a light reflecting film,or the like can be formed on surfaces of the conductor wirings 18A and18B.

The covering member 15 is preferably formed of an insulating material.Examples of the material of the covering member 15 include the samematerials as those described above as examples of the material of thesubstrate 11. Using the resin described above containing white filler orthe like for the covering member 15 allows the light emitted from thelight source 12 to be reflected at the covering member 15, so that thelight extraction efficiency of the planar light source 10 can beimproved.

Light Source 12

The plurality of light sources 12 are disposed two-dimensionally in afirst direction and in a second direction perpendicular to the firstdirection, on the substrate 11 in a plan view. More specifically, asshown in, for example, FIG. 1 , the light sources 12 are arranged in aplurality of first arrays of the light sources each extending along thefirst direction and a plurality of second arrays of the light sourceseach extending along the second direction perpendicular to the firstdirection in the plan view. The first direction and the second directionare, for example, the X direction and the Y direction of FIG. 1 , etc.

The light source 12 is a member configured to emit light, and examplesof the light source 12 include a light emitting element configured toemit light, a light emitting element sealed with a light-transmissiveresin or the like, and a surface-mounted light emitting device (whichmay also be referred to as an LED) in which the light emitting elementis packaged. Examples of the light source 12 include, as illustrated inFIG. 6 , the light emitting element 12 a covered by a sealing member 12b. A single light emitting element 12 a can be used for the light source12, but a plurality of light emitting elements can be used for thesingle light source 12. Further, the light source 12 can have aconfiguration including a resin containing a light-reflective materialand surrounding lateral surfaces of the light emitting element, and alight-transmissive member that covers an upper surface of the lightemitting clement and an upper surface of the resin containing thelight-reflective material. The light source 12 can have a configurationincluding a light-transmissive member covering the upper surface of thelight emitting element and a resin containing a light-reflectivematerial and surrounding the lateral surfaces of the light emittingelement and lateral surfaces of the light-transmissive member. Thelight-transmissive member in an example herein can contain a phosphor. Alight-transmissive bonding member that adheres the light emittingelement and the light-transmissive member can be disposed between thelight emitting element and the light-transmissive member.

The light source 12 can have any appropriate light distributioncharacteristics, but preferably has a wide light distribution in orderto illuminate in each section C surrounded by corresponding portions ofthe wall portion 13 b of the partition member 13 with less unevenness inbrightness. In particular, each of the light sources 12 preferably hasbatwing light distribution characteristics. With such a lightdistribution, the amount of light to be emitted directly above the lightsource 12 can be reduced, and the light distribution of each of thelight sources 12 can be spread, and the wall portion 13 b and bottomportions 13 c can be irradiated with the spread light, so thatunevenness in brightness in each of the sections C surrounded bycorresponding portions of the wall portion 13 b can be reduced.

As used herein, the batwing light distribution characteristics aredefined as characteristics having a light emission intensitydistribution in which the light emission intensity at light distributionangles with an absolute value greater than 0° is greater than that at0°, where an angle of an optical axis OA is 0°. The optical axis OA isdefined by a line passing through the center of the light source 12 andperpendicularly intersecting the upper surface 11 m of the substrate 11,as illustrated in FIG. 6 .

In particular, as illustrated in FIG. 6 , an example of the light source12 having the batwing light distribution characteristics includes thelight emitting element 12 a including a light reflecting film 12 c on anupper surface thereof. With the light reflecting film 12 c disposed onthe upper surface of the light emitting element 12 a, most of the upwardlight from the light emitting element 12 a is reflected at the lightreflecting film 12 c to reduce the amount alight directly above thelight emitting element 12 a, so that the batwing light distributioncharacteristics can be obtained. The light reflecting film 12 c can bedisposed directly on the light emitting element 12 a, so that it is notnecessary to separately combine a special lens for the batwing lightdistribution, which allows for reducing a thickness of the light source12.

The light reflecting film 12 c can be a metal film made of silver orcopper, a resin containing white filler or the like, a combinationthereof, or the like. Alternatively, the light reflecting film 12 c canbe an organic multilayer film (DBR film) and can have an incident angledependence of reflectance for the emission wavelength of the lightemitting element 12 a. More specifically, the reflectance of the lightreflecting film 12 c is preferably set to be lower in the obliqueincidence than in the vertical incidence. With such a reflectance,variation in the brightness immediately above the light emitting element12 a can be gradual, and it is possible to prevent the area immediatelyabove the light emitting element 12 a from being excessively dark, e.g.,becoming a dark spot.

For the light source 12, for example, the light emitting element 12 amounted directly on the substrate 11 has a height in a range of 100 μmto 500 μm. The light reflecting film 12 c can have a thickness in arange of 0.1 μm to 3.0 μm. Even when the sealing member 12 b isincluded, the light source 12 can have a thickness approximately in arange of 0.5 mm to 2.0 mm.

The plurality of light sources 12 are preferably wired on the substrate11 such that the plurality of light sources 12 can be driven separatelyfrom each other and dimming control (e.g., local dimming or high dynamicrange) can be performed for each light source 12.

Light Emitting Element 12 a

A known light emitting element can be used for the light emittingelement 12 a. For example, a light emitting diode is preferably used forthe light emitting element 12 a. A light emitting element having anyappropriate wavelength can be selected for the light emitting element 12a. For example, for a blue or green light emitting element, a lightemitting element using a nitride-based semiconductor such as GaN, InGaN,AlGaN, and AlInGaN can be used. For a red light emitting element,GaAlAs, AlInGaP, and the like can be used. A semiconductor lightemitting element made of a material other than these can also be used.The composition, light emission color, size, number, and the like of thelight emitting elements to be used can be appropriately selectedaccording to the purpose.

As illustrated in FIG. 6 , the light emitting element 12 a can beflip-chip mounted straddling a pair of positive and negative conductorwirings 18A and 18B on the upper surface 11 m of the substrate 11 usingbonding members 19 disposed between the light emitting element 12 a andthe substrate 11. Alternatively, the light emitting element 12 a can beface-up mounted instead of being flip-chip mounted.

The bonding member 19 is a member for securing the light emittingelement 12 a to the substrate or the conductor wirings, and examplesthereof include an insulating resin and a conductive member. In a caseof flip-chip mounting as illustrated in FIG. 6 , a conductive member isused. Specific examples thereof include Au-containing alloys,Ag-containing Pd-containing alloys, In-containing alloys,Pb-Pd-containing alloy, Au—Ga-containing alloys, Au—Sn-containingalloys, Sn-containing alloys, Sn—Cu-containing alloys,Sn-Cu-Ag-containing alloys, Au—Ge-containing alloys, Au—Si-containingalloys, Al-containing alloys, Cu—In containing alloys, and mixtures ofmetals and fluxes.

Sealing Member 12 b

The sealing member 12 b covers the light emitting element 12 a for thepurpose of protecting the light emitting element 12 a from the externalenvironment, optically controlling the light to be emitted from thelight emitting element 12 a (for example, obtaining the batwing lightdistribution characteristics), and the like. For the sealing member 12b, a light-transmissive material is used. Examples of a material of thesealing member 12 b include a light-transmissive resin such as an epoxyresin, a silicone resin, or a resin obtained by mixing them, glass, andthe like, Of these, the silicone resin is preferably used inconsideration of light resistance and ease of molding. The sealingmember 12 b can contain a diffusing agent for diffusing light from thelight emitting element 12 a, a coloring agent corresponding to the lightemitting color of the light emitting element 12 a, and the like. For thediffusing agent, the coloring agent, and the like, those known in theart can be employed.

The sealing member 12 b can be in direct contact with the substrate 11.The sealing member 12 b is adjusted to have a viscosity that allowsprinting, coating with a dispenser, and the like, and can be cured byheat treatment or light irradiation. Examples of the shape of thesealing member 12 b include a substantially hemispherical shape, avertically elongated protruding shape in a cross-sectional view, a flatprotruding shape in a cross-sectional view, and a circular shape or anelliptical shape in a plan view. As used herein, the term “verticallylong protruding shape” refers to a shape, in a cross-sectional view, inwhich the maximum length in the direction perpendicular to the uppersurface 11 m of the substrate 11 is greater than the maximum length inthe direction parallel to the upper surface urn of the substrate 11.Further, the term “flat protruding shape” as used herein refers to ashape, in a cross-sectional view, in which the maximum length in thedirection parallel to the upper surface 11 m of the substrate 11 isgreater than the maximum length in the direction perpendicular to theupper surface 11 m of the substrate 11. The sealing member 12 b can bedisposed to serve as an underfill 12 d between the lower surface of thelight emitting element 12 a and the upper surface 11 m of the substrate11.

Partition Member 13

The wall portion 13 b of the partition member 13 can be in a gridpattern in a plan view. In a plan view, the boundary between adjacentsections C can be regarded as the top portion 13 a. The partition member13 preferably includes the bottom portions 13 c connected to the lowerend of the wall portion 13 b in respective sections C. In other words,in the partition member 13, it is preferable that each section C isconstituted by a corresponding one of the bottom portions 13 c andcorresponding portions of the wall portion 13 b. Peripheral ones of thebottom portions 13 c can extend to the peripheral region of thesubstrate 11 in a plan view. In this case, the peripheral bottomportions 13 c can be located closer to the outer edge of the substrate11 than peripheral portions of the wall portion 13 b. The peripheralregion of the partition member 13 can have a portion that overlaps withthe peripheral region of the substrate 11. The partition member 13 ispreferably a reflective member.

The partition member 13 includes, for example, a through hole 13 d inwhich the light source 12 is disposed at substantially the center of thebottom portion 13 c in the section C. As illustrated in FIG. 6 , thelight source 12 is preferably disposed in the through hole 13 d. Thethrough hole 13 d can have any appropriate shape and size that allowsthe entire light source 12 to be exposed, and the outer edge of thethrough hole 13 d is preferably set to be located only in the vicinityof the light source 12. With this structure, when the partition member13 has light-reflectivity, the light from the light source 12 can bereflected also at the bottom portion 13 c, so that the light extractionefficiency can be improved.

The top portion 13 a is a portion of the wall portion 13 b located atthe greatest height. The top portion 13 a can be a flat surface, but thevicinity of the top portion 13 a preferably has a ridge shape. That is,the vertical cross section of a portion of the wall portion 13 bconstituting the top portion 13 a preferably forms an acute-angledtriangle, and more preferably an acute-angled isosceles triangle.

An acute angle of the acute-angled triangle or the acute-angledisosceles triangle that is an angle of the wall portion 13 b at the topportion 13 a (α in FIG. 6 ) is preferably in a range of 60° to 90°, forexample. With such a range, the space and area occupied by the partitionmember 13 can be reduced, and the height of the partition member 13 canbe reduced, so that size and thickness of the planar light source 10 canbe reduced.

A pitch P, which is an interval between the opposite portions of topportion 13 a of the partition member 13, can be appropriately adjustedaccording to the size of the light source to be used, the intended sizeand performance of the planar light source, and the like. The pitch Pcan be, for example, in a range of 1 mm to 50 mm, preferably in a rangeof 5 mm to 20 mm, and more preferably in a range of 6 mm to 15 mm. Ineach section C, surfaces of the wall portion 13 b on the section C sideinclined spreading upwardly from the bottom portion 13 c and thevicinity of the upper surface 11 m of the substrate 11 can constitutecorresponding portions of the wall portion 13 b that surround acorresponding light source 12.

In addition, the partition member 13 preferably has a height, that is, alength between the lower surface of the bottom portion 13 c and the topportion 13 a of 8 mm or less, and when a thinner planar light source isconfigured, preferably in a range of approximately 1 mm to 4 mm.Further, the distance between the lower surface of the bottom portion 13c of the partition member 13 and the light diffusion plate 14 ispreferably approximately 8 mm or less, and when a thinner planar lightsource is configured, the distance is preferably in a range ofapproximately 2 mm to 4 mm. Accordingly, a thickness of the backlightunit including the optical member such as the light diffusion plate 14can be greatly reduced. The partition member 13 can have a thickness,for example, in a range of 100 μm to 300 μm.

The shape of each section C formed by corresponding portions of thepartition member 13 surrounding the light source 12, that is, the shapeof each of regions demarcated by the wall portion 13 b can be aquadrangular shape in a plan view, or any other appropriate shapes. Forexample, the shape of the section C can be circular, elliptical, or thelike. In order to efficiently dispose the plurality of light sources 12,a polygonal shape such as a triangular shape, a quadrangular shape, or ahexagonal shape is preferable. This allows for facilitating demarcatingthe light emitting area into any number of regions by the wall portion13 b according to the area dimension of the light emitting surface ofthe planar light source 10, and the light emitting area can be disposedat a high density.

The number of sections C demarcated by the wall portion 13 b can be setto any appropriate number, and the shape and arrangement of the wallportion 13 b, the number of sections C, and the like can be changedaccording to the desired size of the planar light source. According tothe number and positions of the light sources 12 disposed on thesubstrate 11 in a plan view, the partition member 13 can have variousshapes, for example, the shapes in which three sections C are adjacentto each other and three end portions of the top portion meet at onepoint, four sections C are adjacent to each other and four end portionsof the top portion meet as illustrated in FIG. 2 , and six sections Care adjacent to each other and six end portions of the top portion meatat one point. When the four sections C are adjacent to each other andthe four end portions of the top portion meet, the section C has aquadrangular shape in a plan view is.

The partition member 13 is preferably disposed on the substrate 11, andthe lower surface of the bottom portion 13 c of the partition member 13and the upper surface 11 m of the substrate 11 are preferably secured toeach other. In particular, these are preferably secured at the peripheryof the through hole 13 d using a light-reflective adhesive member sothat the light emitted from the light source 12 does not enter a spacebetween the substrate 11 and the partition member 13. For example, thelight-reflective adhesive member is more preferably disposed in a ringshape along the outer periphery of the through hole 13 d. The adhesivemember can be a double-sided tape, a hot melt adhesive sheet, or aresin-based adhesive such as a thermosetting resin, a thermoplasticresin, or the like. These adhesive members preferably have high flameresistance. However, the partition member 13 can be secured on thesubstrate 11 by screwing or the like.

As described above, the partition member 13 preferably has the lightreflectivity. This allows light emitted from the light source 12 to beefficiently reflected at the wall portion 13 b and the bottom portion 13c. In particular, when the wall portion 13 b has the inclination asdescribed above and is irradiated with the light emitted from the lightsource 12, the light can be reflected upward. Thus, when the light isnot emitted in an adjacent section C, the contrast ratio can be furtherimproved. Further, the light can be reflected upward more efficiently.

The partition member 13 can be obtained by molding a resin or the likecontaining a reflective material composed of metal oxide particles madeof titanium oxide, aluminum oxide, silicon oxide or the like, or bymolding a resin containing no reflective material and then disposing areflective member on a surface of the molded resin. Alternatively, aresin containing a plurality of fine bubbles can be used for partitionmember 13. In this case, light is reflected at the interface of thebubbles. Further, examples of the resin to be used for the partitionmember 13 include a thermoplastic resin such as an acrylic resin, apolycarbonate resin, a cyclic polyolefin resin, polyethyleneterephthalate (PET), or polyester, and a thermosetting resin such asepoxy or silicone. The partition member 13 is preferably set to have areflectance of 70% or greater to the light emitted from the light source12.

The partition member 13 can be formed by using a molding technique usinga mold, a molding technique using stereolithography, or the like. Forthe molding technique using the mold, molding techniques such asinjection molding, extrusion molding, compression molding, vacuumforming, pressure forming, and press forming can be employed. Forexample, the partition member 13 in which the bottom portions 13 c andthe wall portion 13 b are integrally formed can be formed by vacuumforming using a reflective sheet formed of PET or the like.

Light Diffusion Plate 14

The light diffusion plate 14 is a member having an irregular shape thatdiffuses and transmits incident light, and one light diffusion plate 14can be disposed above the plurality of light sources 12. The lightdiffusion plate 14 is preferably a flat plate-shaped member, but mayalternatively have protrusions and/or recesses in a surface thereof. Thelight diffusion plate 14 is preferably disposed substantially parallelto the substrate 11.

When the pitch between the portions of the top portion 13 a of thepartition member 13 is P [mm], the light diffusion plate 14 ispreferably disposed so that a distance OD between the light diffusionplate 14 and the light source 12 is, for example, 0.3P [mm] or less, andmore preferably 0.25P [mm] or less. As used herein, as illustrated inFIG. 6 , the distance OD refers to a distance between the outermostsurface of the substrate 11 (that is, when the substrate 11 has acoating layer, wiring layer, or the like at a surface thereof, theoutermost surface of the coating layer, wiring layer, or the like) andthe lower surface of the light diffusion plate 14. From anotherperspective, the light diffusion plate 14 is preferably disposed suchthat a distance H between the light diffusion plate 14 and the uppersurface of the bottom portion 13 c of the partition member 13,illustrated in FIG. 6 , is in a range of 1.5 mm to 5 mm, more preferablyin a range of 2 mm to 3 mm.

The light diffusion plate 14 can be made of a material having low lightabsorption for visible light, such as a polycarbonate resin, apolystyrene resin, an acrylic resin, or a polyethylene resin. To diffusethe incident light, a surface of the light diffusion plate 14 can haveprotrusions and recesses, or a material having a refractive indexdifferent from that of a base material of the light diffusion plate 14can be dispersed in the light diffusion plate 14. The protrusions andrecesses can be made, for example, in a size of 0.01 mm to 0.1 mm. Forthe material having the different refractive index, for example, apolycarbonate resin, an acrylic resin, or the like can be selected to beused.

A thickness of the light diffusion plate 14 and the degree of lightdiffusion of the light diffusion plate 14 can be appropriately set, andcommercially available members such as a light diffusion sheet or adiffuser film can be used for the light diffusion plate 14. For example,the thickest portion of the light diffusion plate 14 can have athickness in a range of 1 mm to 2 mm.

In the planar light source 10, with the substrate 11 having an irregularshape, when as many light sources 12 as possible are disposed on thesubstrate 11 while maintaining the matrix arrangement in the firstdirection and the second direction, a region on which no light source 12is disposed may be generated on the substrate 11 near the outerperiphery of the substrate 11. Then, if no measures are taken, theperipheral region of the planar light source 10 (for example, the areabetween the outermost periphery of the partition member 13 and the outeredge of the light diffusion plate 14) would become a dark portion, andthe peripheral region of the planar light source may have unevenness inbrightness. In FIG. 1 , for example, the dark portions would benoticeable in regions surrounded by the long dashed double-short dashedlines F. That is, if no measures are taken, unevenness in brightnesswill occur in a part of the peripheral region of the planar light source10. In view of this, in the planar light source 10, a part of theperipheral region of the light diffusion plate 14 is thinner than thecentral side of the light diffusion plate 14 to reduce the occurrence ofunevenness in brightness. When necessary, the entire peripheral regionof the light diffusion plate 14 can be thinner than the central side ofthe light diffusion plate 14. Hereinafter, the shape of the lightdiffusion plate 14 will be described in detail.

The light diffusion plate 14 includes a thick plate portion 14 a and athin plate portion 14 b having a thinner thickness than the thick plateportion 14 a, and the thick plate portion 14 a and the thin plateportion 14 b are disposed adjacent to each other and integrally formedas a single body. In FIG. 5 , for convenience, the thick plate portion14 a is illustrated in white and the thin plate portion 14 b isillustrated in a dot pattern. The light diffusion plate 14 can beconstituted by a single piece, or can be constituted by two or morelayers. When the light diffusion plate 14 is constituted by two layers,for example, a second layer having a width narrower than that of thefirst layer can be provided on the first layer that is located closer tothe substrate. In this structure, a region where the second layer isdisposed on the first layer can serve as the thick plate portion 14 a,and a region where the second layer is not disposed on the first layercan serve as the thin plate portion 14 b.

A boundary 14 c between the thick plate portion 14 a and the thin plateportion 14 b is located, for example, at a position facing peripheralportions of the wall portion 13 b of the partition member 13. With thisstructure, on an outer peripheral side with respect to the peripheralportions of the wall portion 13 b of the partition member 13, thefrequency of light diffusion can be reduced and the amount of lighttransmitted through the thin plate portion 14 b can be increased. Thiscan result in a reduction in the occurrence of unevenness in brightnessat the peripheral region of the planar light source 10. The boundary 14c can be located at a position facing the peripheral portions of the topportion 13 a of the partition member 13.

When the wail portion 13 b is located at a position directly below theboundary between the thick plate portion 14 a and the thin plate portion14 b of the light diffusion plate 14 (FIG. 3 ) or its vicinity, a lightemitted from the light source 12 toward the thin plate portion 14 b ofthe light diffusion plate 14 is diffused in the thick plate portion 14 aof the light diffusion plate 14, and then a portion of the diffusedlight is incident on the thin plate portion 14 b. With a smallerthickness of the thin plate portion 14 b, the light incident on the thinplate portion 14 b is diffused at less frequency. Accordingly, the lightextraction in the thin plate portion 14 b is improved.

The thin plate portion 14 b preferably has a thickness 0.5 times or lessthe thickness of the thick plate portion 14 a. With such a thickness,the amount of light extracted from the area of the thin plate portion 14b increases, so that the occurrence of unevenness in brightness at theperipheral region of the planar light source 10 can be reduced.

A lower surface 14 n of the thick plate portion 14 a (a surface on thelight source 12 side) and a lower surface 14 t of the thin plate portion14 b (a surface on the light source 12 side) are in the same plane, andan upper surface 14 m of the thick plate portion 14 a (a surfaceopposite to the surface on the light source 12 side) and an uppersurface 14 s of the thin plate portion 14 b (a surface opposite to thesurface on the light source 12 side) are located at positions differentin the height direction.

That is, the height from the upper surface 11 m of the substrate 11 tothe lower surface 14 t of the thin plate portion 14 b is the same as theheight from the upper surface 11 m of the substrate 11 to the lowersurface 14 n of the thick plate portion 14 a. On the other hand, theheight from the upper surface 11 m of the substrate 11 to the uppersurface 14 s of the thin plate portion 14 b is smaller than the heightfrom the upper surface 11 m of the substrate 11 to the upper surface 14m of the thick plate portion 14 a.

The thin plate portion 14 b is located in at least a part of theperipheral region of the light diffusion plate 14 in a plan view. Asillustrated in FIG. 5 , in the present embodiment, as an example, thethin plate portion 14 b is provided over the entire peripheral region ofthe light diffusion plate 14 (the portion indicated by the dot pattern).With the thin plate portion 14 b is provided over the entire peripheralregion of the light diffusion plate 14, the brightness of the entireperipheral region of the light diffusion plate 14 can be increased, sothat the unevenness in brightness can be reduced. Alternatively, astructure in which the thin plate portion 14 b is located only in a partof the peripheral region of the light diffusion plate 14 may beemployed.

In the planar light source 10, in a plan view, the greater the distancebetween the optical axis of a peripheral one of the light sources 12 inthe X direction and a corresponding portion on the outer edge of thelight diffusion plate 14 in the X direction, the greater the width of acorresponding portion of the thin plate portion 14 b in the X direction.In FIG. 7 , the structures under the light diffusion plate 14 (i.e., thesubstrate 11, the light sources 12, and the partition member 13) areillustrated with solid lines in order to better show these structures.For example, as illustrated in FIG. 7 , the plurality of light sources12 include one first distal-end light source 12 ₁, which is an outermostone of the light sources in one of the first arrays of light sources 12extending along the X direction, and another first distal-end lightsource 12 ₂, which is an outermost one of the light sources in anotherof the first arrays of light sources 12 extending along the X direction,and a distance L₁ between an optical axis OA₁ of the one firstdistal-end light source 12 ₁ and the outer edge of the light diffusionplate 14 in the X direction is greater than a distance L₂ between anoptical axis OA₂ of the another first distal-end light source 12 ₂ andthe outer edge of the light diffusion plate 14 in the X direction. Inthis case, as illustrated in FIG. 8 , in a plan view, a width W₁ of thethin plate portion 14 b as measured along a straight line extendingalong the X direction from the optical axis OA₁ of the one firstdistal-end light source 12 ₁ toward the outer edge of the lightdiffusion plate 14 is greater than a width W₂ of the thin plate portion14 b as measured along a straight line extending along the X directionfrom the optical axis OA₂ of the another first distal-end light source12 ₂ toward the outer edge of the light diffusion plate 14.

Further, in a plan view, the greater the distance between the opticalaxis of a distal-end light source 12 in the Y direction and acorresponding portion on the outer edge of the light diffusion plate inthe Y direction, the greater the width of a corresponding portion of thethin plate portion 14 b in the Y direction. For example, as illustratedin FIG. 7 , the plurality of light sources 12 include one seconddistal-end light source 12 ₃, which is an outermost one of the lightsources in one of the second arrays of light sources 12 extending alongthe Y direction, and another second distal-end light source 12 ₄, whichis an outermost one of the light sources in another of the second arraysof light sources 12 extending along the Y direction, and a distance L₃between an optical axis OA₃ of the one second distal-end light source 12₃ and the outer edge of the light diffusion plate 14 in the Y directionis greater than a distance L₄ between an optical axis OA₄ of the anothersecond distal-end light source 12 ₄ and the outer edge of the lightdiffusion plate 14 in the Y direction. In this case, as illustrated inFIG. 8 , in a plan view, a width W₃ of the thin plate portion 14 b asmeasured along a straight line extending along the Y direction from theoptical axis OA₃ of the one second distal-end light source 12 ₃ towardthe outer edge of the light diffusion plate 14 is greater than a widthW₄ of the thin plate portion 14 b as measured along a straight lineextending along the Y direction from the optical axis OA₄ of the anothersecond distal-end light source 12 ₄ toward the outer edge of the lightdiffusion plate 14.

FIGS. 9 and 10 are diagrams showing the results of simulations for thelight diffusion plates. FIG. 9 shows the simulation result of the planarlight source 10, and FIG. 10 shows the simulation result of a planarlight source 10X provided with a light diffusion plate 14X having aconstant thickness instead of the light diffusion plate 14 of the planarlight source 10 (comparative example). In FIGS. 9 and 10 , a largenumber of thin lines indicate light rays.

Comparing the portions surrounded by the broken lines in FIGS. 9 and 10, it can be confirmed that the planar light source 10 provided with thethin plate portion 14 b has greater density of light rays, and allowsbetter light extraction at the peripheral region of the light diffusionplate 14 than the planar light source 10X not provided with the thinplate portion. That is, it can be confirmed that the unevenness in thebrightness of the light emitting surface at the peripheral region of thelight diffusion plate 14 can be reduced. This is because providing thethin plate portion 14 b to the light diffusion plate 14 allows forreducing the frequency of light diffusion at a location of the thinplate portion 14 b, which allows for increasing the amount of lighttransmitted through the location of the thin plate portion 14 b. This isalso because light emitted from a lateral surface of the thick plateportion 14 a exposed toward the thin plate portion 14 b and light passedthrough the thin plate portion 14 b and reflected on a lateral surfaceof the thick plate portion 14 a propagate toward the upper surface sideof the light diffusion plate, which allows for increasing the density ofthe light on the upper surface side of the light diffusion plate.

For the light diffusion plate 14, a simulation was performed with athickness of the thick plate portion 14 a set to 1.2 mm and a thicknessof the thin plate portion 14 b varied to 0.4 mm, 0.2 mm, and 0.1 mm, andthen the brightness of the light transmitted through the thin plateportion 14 b in a region of the thin plate portion 14 b was calculated.As shown in Table 1, in a case in which the thin plate portion 14 b was0.4 mm, the brightness was increased by 1.1 times as compared with acase in which the thin plate portion 14 b was 1.2 mm (that is, when thethin plate portion 14 b had the same thickness as the thick plateportion 14 a). Similarly, in a case in which the thin plate portion 14 bwas 0.2 mm, the brightness was increased by 1.12 times. Further, in acase in which the thin plate portion 14 b was 0.1 mm, the brightness wasincreased by 1.17 times.

TABLE 1 BRIGHTNESS RATIO OF LIGHT TRANSMITTED THROUGH THIN THICKNESS OFTHIN PLATE PLATE PORTION 14b IN AREA OF PORTION 14b (mm) THIN PLATEPORTION 14b 1.2 1.00 0.4 1.10 0.2 1.12 0.1 1.17Furthermore, when comparing the light leaking to the outside through alateral surface of the light diffusion plate, it can be confirmed thatthe planar light source 10 provided with the thin plate portion 14 b isless likely to leak the light compared to a case in which the planarlight source 10X not provided with the thin plate portion is used. Thatis, in the planar light source 10, the light that would laterally leakin a conventional technique can be propagated to the upper surface sideof the light diffusion plate 14. Accordingly, along with a reduction inthe frequency of light diffusion in the thin plate portion 14 b, thedensity of the light rays on the upper surface side of the thin plateportion 14 b can be increased.

Further, in the planar light source 10, with the thin plate portion 14 bdisposed on the light diffusion plate 14, the amount of light leakingfrom the lateral surface of the light diffusion plate 14 can be reduced.

In the planar light source 10, a wavelength conversion sheet adapted toconvert light from the light source 12 into light having a differentwavelength can be disposed above the light diffusion plate 14. In thecase in which the wavelength conversion sheet is disposed above thelight diffusion plate 14, when light leaks from the lateral surface ofthe light diffusion plate, an end portion of the planar light source maybe seen in the emission color (for example, blue) of the light emittingelement 12 a. However, in the planar light source 10, the lightdiffusion plate 14 includes the thin plate portion 14 b, which allowsfor reducing the amount of light leaking from the lateral surface of thelight diffusion plate 14, so that the phenomenon that the end portion ofthe planar light source 10 is seen in the emission color of the lightemitting element 12 a can be reduced. That is, when disposing thewavelength conversion sheet above the light diffusion plate 14, thephenomenon that light having a wavelength different from a wavelengthresulting from conversion by the wavelength conversion sheet leaks tothe outside through the lateral surface of the light diffusion plate 14can be reduced.

As described above, in the planar light source 10, with the substrate 11having the irregular shape, when as many light sources 12 as possibleare placed on the substrate 11 while maintaining the matrix arrangementin the first direction and the second direction, there is a region nearthe outer edge of the substrate 11 where the light source 12 is notdisposed. Then, when no measures are taken, for example, the regionbetween the outermost periphery of the partition member 13 and the outeredge of the light diffusion plate 14 becomes a dark portion. That is,when no measures are taken, unevenness in brightness will occur in apart of the peripheral region of the planar light source 10. However,with the thin plate portion 14 b located in the peripheral region of thelight diffusion plate 14, light extraction is prioritized over lightdiffusion in the thin plate portion 14 b. Accordingly, the frequency oflight diffusion can be reduced, and the amount of light transmittedthrough the thin plate portion 14 b can be increased. As a result, theoccurrence of unevenness in brightness at the peripheral region of theplanar light source 10 can be reduced.

The thin plate portion 14 b can be provided in a portion whereunevenness in brightness may occur, and thus the thin plate portion 14 bneed not be provided over the entire peripheral region of the lightdiffusion plate 14, and the thin plate portion 14 b can be provided onlyin a part of the peripheral region of the light diffusion plate 14.

In addition, for the similar reason, in both the X direction and the Ydirection, it is not necessary that the greater a distance between anoptical axis of a distal-end light source 12 and a corresponding portionon the outer edge of the light diffusion plate 14, the greater the widthof the thin plate portion 14 b. That is, in at least one of the Xdirection and the Y direction, the greater the distance between theoptical axis of a distal-end light source 12 and the outer edge of thelight diffusion plate 14, the greater a width of the thin plate portion14 b

The planar light source 10 can include, above the light diffusion plate14, at least one type of sheet selected from the group consisting of awavelength conversion sheet adapted to convert light from the lightsource 12 into light having a different wavelength, a prism sheet, and apolarizing sheet. More specifically, as illustrated in FIG. 11 , opticalmembers such as a wavelength conversion sheet 72, prism sheets (a firstprism sheet 73 and a second prism sheet 74), a polarizing sheet 75, andthe like can be disposed above the light diffusion plate 14 at apredetermined distance or directly or indirectly on the upper surface ofthe light diffusion plate 14, and a liquid crystal panel can be furtherdisposed on the optical members, so that a surface emitting lightemitting device to be used as a light source for a direct backlight canbe obtained. The order of layering these optical members can be set asdesired.

Wavelength Conversion Sheet 72

While the wavelength conversion sheet 72 can be disposed on either theupper surface or the lower surface of the light diffusion plate 14, asillustrated in FIG. 11 , the wavelength conversion sheet 72 ispreferably disposed on the upper surface of the light diffusion plate14. The wavelength conversion sheet 72 is adapted to absorb a portion oflight emitted from the light source 12 and emit light having awavelength different from the wavelength of the light emitted from thelight source 12. For example, the wavelength conversion sheet 72 isadapted to absorb a portion of blue light emitted from the light source12 and emit yellow light, green light, and/or red light, so that theplanar light source 10 adapted to emit white light can be obtained. Thewavelength conversion sheet 72 is disposed spaced apart from the lightemitting element 12 a of the light source 12, so that a phosphor or thelike having poor resistance to heat or light intensity, which isdifficult to use in the vicinity of the light emitting element 12 a, canbe used for the wavelength conversion sheet 72. Consequently, theperformance of the planar light source 10 as a backlight can beimproved. The wavelength conversion sheet 72 has a sheet shape or alayered shape, and includes the phosphor or the like described above.The wavelength conversion sheet may be referred to as a wavelengthconversion layer.

First Prism Sheet 73 and Second Prism Sheet 74

The first prism sheet 73 and the second prism sheet 74 have a shape inwhich a plurality of prisms extending in a predetermined direction aredisposed in surfaces thereof. For example, when each of the first andsecond prism sheets 73 and 74 is viewed in two dimensions consisting ofthe X direction and the Y direction perpendicular to the X direction,the first prism sheet 73 can have a plurality of prisms extending alongthe Y direction, and the second prism sheet 74 can have a plurality ofprisms extending along the X direction. The first prism sheet 73 and thesecond prism sheet 74 are configured to refract incident light,propagated in various directions, toward the display panel facing theplanar light source 10. Accordingly, light emitted from the lightemitting surface of the planar light source 10 can be emitted mainly ina direction perpendicular to the upper surface of the light emittingsurface, and the brightness when the planar light source 10 is viewed ina front view can be increased.

Polarizing Sheet 75

For example, the polarizing sheet 75 is configured to selectivelytransmit light in a polarization direction that matches the polarizationdirection of a polarizing plate disposed proximate to the backlight of adisplay panel such as a liquid crystal display panel, and to reflectpolarized light in a direction perpendicular to the polarizationdirection toward the first prism sheet 73 and the second prism sheet 74.A portion of the polarized light returned from the polarizing sheet 75is reflected at the first prism sheet 73, the second prism sheet 74, thewavelength conversion sheet 72, and the light diffusion plate 14. Atthis time, the reflected light changes in the polarization direction,for example, is converted into polarized light having the polarizationdirection of the polarizing plate of the liquid crystal display panel,is again incident on the polarizing sheet 75, and is emitted to thedisplay panel. Accordingly, the polarization direction of the lightemitted from the planar light source 10 can be aligned, and light in thepolarization direction effective for enhancing the brightness of thedisplay panel can be emitted with high efficiency. For the polarizingsheet 75, the first prism sheet 73, the second prism sheet 74, and thelike, commercially available optical members for backlights can be used.

In the planar light source 10, instead of providing the wavelengthconversion sheet 72, the sealing member 12 b can contain a wavelengthconversion material such as phosphor adapted to absorb light emittedfrom the light emitting element 12 a and to emit light having awavelength different from that of the outputted light from the lightemitting element 12 a. With this structure, the sealing member 12 babsorbs a portion of blue light emitted from the light source 12 andemits yellow light, green light, and/or red light, so that the planarlight source 10 configured to emit white light can be obtained.

In addition to the wavelength conversion material, the sealing member 12b can contain a diffusing agent for diffusing light emitted from thelight emitting element 12 a, a coloring agent corresponding to theemission color of the light emitting element 12 a, and the like. For thediffusing agent, the coloring agent, and the like, those known in theart can be employed. Further, instead of a structure in which thesealing member 12 b contains the wavelength conversion material such asa phosphor, for example, a light emitting element 12 a in which anitride-based semiconductor is covered by a wavelength conversionmaterial such as a phosphor, that is, the light emitting element 12 aconfigured to emit white light can be used.

First Modified Example of First Embodiment

In the first modified example of the first embodiment, an example inwhich the cross-sectional shape of the thin plate portion of the lightdiffusion plate is different from that of the first embodiment will beillustrated. In description of the first modified example of the firstembodiment, repetitive description of the same components as those ofthe embodiment described above may be omitted.

FIGS. 12 to 14 are schematic partially enlarged cross-sectional viewsillustrating different examples of light diffusion plates of the planarlight source according to the first modified example of the firstembodiment. FIG. 15 is a schematic plan view illustrating the lightdiffusion plate of FIG. 14 .

In a light diffusion plate 24 illustrated in FIG. 12 , the height fromthe upper surface 11 m of the substrate 11 to a lower surface 24 t of athin plate portion 24 b is the same as the height from the upper surface11 m of the substrate 11 to a lower surface 24 n of a thick plateportion 24 a. In addition, the thickness of the thin plate portion 24 bgradually decreases from a boundary 24 c with the thick plate portion 24a toward the outer edge of the light diffusion plate 24.

As described above, the boundary between the thick plate portion and thethin plate portion need not be stepped as illustrated in FIG. 3 , andcan have a shape in which the thickness varies smoothly as illustratedin FIG. 12 . Also with this structure, in the thin plate portion 24 b,light extraction can be prioritized over light diffusion. This allowsfor reducing the frequency of light diffusion, the amount of lighttransmitted through the thin plate portion 24 b can be increased.Accordingly, the occurrence of unevenness in brightness at theperipheral region of the planar light source can be reduced.

Further, instead of the shape of the light diffusion plate 24illustrated in FIG. 12 , in which a thickness of the entire thin plateportion 24 b is gradually decreased, the thin plate portion can have ashape having a portion in which the thickness gradually decreases fromthe boundary with the thick plate portion toward the outer edge of thelight diffusion plate. For example, as in a light diffusion plate 34illustrated in FIG. 13 , a thin plate portion 34 b can have a thicknessgradually decreasing portion 34 b 1 in which the thickness graduallydecreases from a boundary 34 c with a thick plate portion 34 a towardthe outer edge of the light diffusion plate 34, and can further have athickness constant portion 34 b 2 located closer to the outer edge ofthe light diffusion plate 34 than the thickness gradually decreasingportion 34 b 1. The thickness constant portion 34 b 2 has, for example,the same thickness as the thinnest portion of the thickness graduallydecreasing portion 34 b 1.

Also, as in a light diffusion plate 44 illustrated in FIGS. 14 and 15 ,a thin plate portion 44 b can have a first thin plate portion 44 b 1 ona thick plate portion 44 a side, and a second thin plate portion 44 b 2,which is located closer to the outer edge of the light diffusion plate44 than the first thin plate portion 44 b 1 and is thinner than thefirst thin plate portion 44 b 1. With such a two-step variation inthickness of the thin plate portion 44 b, the brightness at the endportion of the planar light source can be increased. That is, becausethe greater the distance from the light source 12, the darker theportion would become, a structure in which the thickness of the lightdiffusion plate 14 is reduced in a direction in which the distance fromthe light source 12 increases allows for reduce the occurrence ofunevenness in brightness at the peripheral region of the planar lightsource. The variation in the thickness of the thin plate portion 44 bcan be in more than two steps. Further, the thin plate portion 44 b canhave a cross-sectional shape in which the shapes illustrated in FIGS. 12to 14 are appropriately combined.

The second thin plate portion 44 b 2 is disposed, for example, closer tothe outer edge of the light diffusion plate 44 than the area where thethrough hole 13 d of the partition member 13 is formed in a plan view.The second thin plate portion 44 b 2 can be disposed in the section Cwhere the light source 12 is not disposed. The boundary 44 c between thefirst thin plate portion 44 b 1 and the second thin plate portion 44 b 2can be located at a position overlapping the top portion 13 a of thepartition member 13 in a plan view.

It is not always necessary to dispose both the first thin plate portion44 b 1 and the second thin plate portion 44 b 2 over the entireperipheral region of the light diffusion plate 44, and a structure maybe employed in which only the first thin plate portion 44 b 1 isdisposed in a region where unevenness in brightness is not likely tooccur. For example, in an area R in which the light sources 12 arelinearly arranged in FIG. 15 , unevenness in brightness is unlikely tooccur, so that it is possible to dispose only the first thin plateportion 44 b 1 in the region R. Alternatively, when the unevenness inbrightness hardly occurs in the region R in which the light sources 12are linearly arranged in FIG. 15 , the thin plate portion 44 b need notbe provided in the region R.

Second Modified Example of First Embodiment

In the second modified example of the first embodiment, an example isillustrated in which the partition member has sections having differentsizes on its peripheral region. In description of the second modifiedexample of the first embodiment, repetitive description of the samecomponents as those of the above-described embodiment may be omitted.

FIG. 16 is a schematic partially enlarged plan view of a partitionmember according to the second modified example of the first embodiment,FIG. 17 is a cross-sectional view taken along line B-B of FIG. 16 . In apartition member 23 illustrated in FIGS. 16 and 17 , portions of a topportion 23 a and portions of a wall portion 23 b, which constituteperipheral sections C of the plurality of sections C, are disposed inthe vicinity of the outer edge of the substrate 11. That is, in at leastone of the peripheral sections C, in a plan view, the area of the areasurrounded by the wall portion 23 b is larger than that of a section Cinward of the peripheral sections C. While a region in a peripheralsection C surrounded by a corresponding portion of the wall portion 23 bthe example of FIGS. 16 and 17 has an area dimension expanded in the Xdirection, such a region can have an area dimension expanded in the Ydirection. Alternatively, the peripheral sections C may include both aperipheral section C in which a region surrounded by a correspondingportion of the wall portion 23 b has an area dimension expanded in the Xdirection and a peripheral section C in which the area dimension of theregion surrounded by a corresponding portion of the wall portion 23 b ofthe peripheral section C is expanded in the Y direction.

As described above, while the area dimension of the bottom portions 23 ceach exposed in a respective section C are equal among all the sectionsC in a plan view in the example of FIGS. 2 and 3 , other arrangement mayalternatively be employed. As in the example of FIGS. 16 and 17 , in aplan view, at least one of the regions surrounded by peripheral portionsof the wall portion 23 b located at the periphery of the partitionmember 23 can have an area dimension larger than that of the areadimension surrounded by a portion of the wall portion 23 b locatedinward of the periphery of the partition member 23.

In the structure of the partition member 23 illustrated in FIGS. 16 and17 , portions of the wall portion 23 b constituting a peripheral sectionC is located in the vicinity of the outer edge of the substrate 11,which allows for improving light extraction toward a light emittingsurface. That is, in the structure of the partition member 23illustrated in FIGS. 16 and 17 , the wall portion 23 b is also locatedon the peripheral region of the substrate 11, so that a greater amountof light can be transmitted to the thin plate portion 14 b of the lightdiffusion plate 14. This can result in a reduction in the occurrence ofunevenness in brightness at the peripheral region of the planar lightsource 10. However, the wall portion 23 b needs not be provided on atleast a part of the periphery of the partition member 23. While the wallportion 23 b of the partition member is not disposed at the boundarybetween the thick plate portion 14 a and the thin plate portion 14 b ofthe light diffusion plate 14 in the example in FIGS. 16 and 17, the wallportion 23 b can be provided at this position.

Third Modified Example of First Embodiment

In the third modified example of the first embodiment, modified examplesof the members other than the light diffusion plate and the partitionmember are illustrated. In the description of the third modified exampleof the first embodiment, repetitive description of the same componentsas those of the above-described embodiment may be omitted.

FIG. 18A is a schematic partially enlarged cross-sectional view in thevicinity of the outer edge of the planar light source. As illustrated inFIG. 18A, the planar light source can have a frame body 26 surroundingthe substrate 11 and the light diffusion plate 14. The frame body 26 hasan irregular shape such as a shape similar to that of the substrate 11,and includes a bottom portion 26 a that is a little larger than thesubstrate 11 in a plan view and a lateral wall 26 b.

A peripheral region of the bottom portion 26 a is annularly exposed tothe outside of the substrate 11, and the lateral wall 26 b is located inthe exposed portion of the bottom portion 26 a to surround the substrate11. A cover 27 surrounding the outer edges of the substrate 11 and thelight diffusion plate 14 can be disposed on the side opposite to thebottom portion 26 a with respect to the lateral wall 26 b. The cover 27is disposed at a position that does not block the light emitted fromeach of the light sources 12. The frame body 26 and the cover 27 can beformed of various materials such as resins containing a reflectivematerial, metals, and ceramics.

As illustrated in FIG. 18B, a wavelength conversion member 28 containinga phosphor can be disposed in a region between the substrate 11 and thelight diffusion plate 14 on inner lateral surfaces of the lateral wall26 b. With this structure, a wavelength of a portion of light emittedfrom the light source 12 is converted by the wavelength conversionmember 28 disposed on the inner lateral surfaces of the lateral wall 26b, and the wavelength converted light is extracted. Therefore, thephenomenon that the end portion of the planar light source 10 is seen inan emission color of the light emitting element can be reduced. When thewavelength conversion member 28 is disposed on the inner lateralsurfaces of the lateral wall 26 b, in the cross-sectional view of theplanar light source, the wall portion 13 b of the partition member 13may or may not be disposed between the light source 12 and the lateralwall 26 b. The wavelength conversion member 28 can be disposed on theentire inner lateral surfaces of the lateral wall 26 b or can bedisposed on the inner lateral surfaces of the lateral wall 26 b in aregion below the lower surface of the light diffusion plate 14. When thewavelength conversion member 28 is disposed in the region below thelower surface of the light diffusion plate 14, the thin plate portion 14b of the light diffusion plate 14 may or may not cover the upper part ofthe wavelength conversion member 28. For the wavelength conversionmember 28, a material that emits yellow light (for example, YAG) can beused. One wavelength conversion member 28 or a plurality of wavelengthconversion members 28 can be disposed on the inner lateral surfaces ofthe lateral wall 26 b.

With the frame body 26 and the cover 27 are provided in the planar lightsource in this arrangement, the substrate 11 and the light diffusionplate 14 can be protected from external impact or the like. The lightdiffusion plate 14, the substrate 11, and the frame body 26 can havesimilar irregular shapes.

FIG. 19 is a schematic plan view explaining an outer shape of asubstrate of the planar light source according to the third modifiedexample of the first embodiment, and illustrates only the substrate, thelight sources, and the partition member. The shape of the lightdiffusion plate can be, for example, the same shape as that of FIG. 5 .A substrate 21 of a planar light source 20 illustrated in FIG. 19 has anirregular shape without a region where the light source 12 is notdisposed as compared with the substrate 11 illustrated in FIG. 1 . Thatis, the substrate 21 has an outermost shape corresponding to theoutermost shape of the partition member 13. In the example of FIG. 19 ,the substrate 21 is located at a position overlapping with the partitionmember 13 (the lower side of the partition member 13) in a plan view.

As described above, the substrate 21 to be used for the planar lightsource can have a shape without a region where the light source 12 isnot disposed. In this case as well, using the light diffusion plate 14having the same shape as that of FIG. 5 allows for decreasing thefrequency of light diffusion at the peripheral region of the lightdiffusion plate 14, so that light to be transmitted through the lightdiffusion plate 14 can be increased. This can result in reduction inoccurrence of unevenness in brightness at the peripheral region of theplanar light source.

The cross-sectional shape of the planar light source 20 can be a linearshape parallel to the XY plane as illustrated in FIG. 11 and the like,or can be a curved shape with respect to the XY plane. For example, thecross-sectional shape of the planar light source 20 can be a curvedshape in which the light emitting surface is recessed in the Xdirection.

Second Embodiment

For a second embodiment, an example of a liquid crystal display deviceusing the planar light source according to the first embodiment as abacklight source will be illustrated. In description of the secondembodiment, repetitive description of the same components as those ofthe embodiment described above may be omitted.

FIG. 20 is a configuration diagram illustrating a liquid crystal displaydevice according to the second embodiment. As illustrated in FIG. 20 , aliquid crystal display device 1000 includes a liquid crystal panel 120,an optical sheet 110, and the planar light source 10 according to thefirst embodiment in this order from the upper side. In the planar lightsource 10, a reference sign 70 denotes the optical members such as thelight diffusion plate and the wavelength conversion sheet. In theexample herein, the optical sheet 110 can be provided with a reflectivepolarizer film (DBEF), a brightness enhancement film (BEF), a colorfilter, or the like, in addition to or instead of some of the opticalmembers.

The liquid crystal display device 1000 is a so-called direct-lit liquidcrystal display device in which the planar light source 10 is layeredbelow the liquid crystal panel 120. In the liquid crystal display device1000, the liquid crystal panel 120 is irradiated with light emitted fromthe planar light source 10. In addition to the above-describedconstituent members, a member such as a color filter can be furtherprovided.

In general, in a direct liquid crystal display device, since thedistance between the liquid crystal panel and the planar light source isshort, the uneven color and the unevenness in the brightness of theplanar light source can affect the uneven color and unevenness in thebrightness of the liquid crystal display device. Therefore, as a planarlight source for a direct liquid crystal display device, a planar lightsource having less uneven color and unevenness in brightness is desired.Using the planar light source 10 for the liquid crystal display device1000 allows for reducing the unevenness in brightness to be generated onthe peripheral region and reducing the overall unevenness in brightnessand emission color while reducing the thickness of the planar lightsource 10 to 5 mm or less, 3 mm or less, 1 mm or less, or the like.

The number of the planar light source 10 used as the backlight for asingle liquid crystal display device 1000 may be other than one, and aplurality of arranged planar light sources 10 can be used for thebacklight for one liquid crystal display device 1000. For example,producing a plurality of small planar light sources 10 and performinginspection or the like on each of them allows for improving the yieldcompared with a case of producing a single large planar light source 10a large number of light sources 12 are mounted.

As described above, the planar light source 10 is configured to emituniform light from the optical member 70, and thus is preferable for useas a backlight for the liquid crystal display device 1000.

The planar light source 10 can also be preferably used as a backlightdevices for televisions, tablets, smartphones, smart watches, head-updisplays, digital signage, bulletin boards, and the like. In addition,the planar light source 10 can also be used as a light source forlighting, and can also be used for emergency lights, linear lighting,various illuminations, vehicle instrument panels, and the like. One ormore modifications illustrated in the first to third modified examplesof the first embodiment can be applied to the planar light source 10.

While certain embodiments and the like have been described in detailabove, the present invention is not limited to the embodiments and thelike described above, various modifications and substitutions can bemade to the embodiments and the like described above without departingfrom the scope described in the claims.

For example, in the embodiment described above, the example in which thelower surface of the thick plate portion of the light diffusion plate(the surface proximate to the light source) and the lower surface of thethin plate portion of the light diffusion plate (surface proximate tothe light source) are on the same plane. However, the upper surface ofthe thick plate portion of the light diffusion plate (a surface on aside opposite to a side where the light source is disposed) and theupper surface of the thin plate portion (a surface on the side oppositeto the side where the light source is disposed) can be in the sameplane. That is, the light diffusion plate can be thinned on its lowersurface side to obtain the thin plate portion. For example, the lightdiffusion plate can have an inverted shape of the light diffusion plate14 illustrated in FIG. 6 , the light diffusion plate 24 illustrated inFIG. 12 , the light diffusion plate 34 illustrated in FIG. 13 , and thelight diffusion plate 44 illustrated in FIG. 14 . In these cases, whileit cannot be expected that the light from a lateral surface of the thickplate portion toward the upper surface side of the light diffusion platewill increase, the frequency alight diffusion in the thin plate portioncan be decreased and the amount of light transmitted through the thinplate portion can be increased, so that a certain effect of reducingunevenness in brightness of the light emitting surface at the peripheralregion of the light diffusion plate can be obtained.

Also, the light diffusion plate can contain scattered particles such astitanium oxide particles or phosphor particles, and the concentration ofscattered particles contained in the thin plate portion can be less thanthe concentration of scattered particles contained in the thick plateportion. Consequently, the frequency of light diffusion in the thinplate portion can be further reduced and light transmitted through thethin plate portion can be further increased, so that the effect ofreducing unevenness in the brightness of the light emitting surface atthe peripheral region of the light diffusion plate can be improved.Alternatively, in a case in which a scattered particle layer containingscattered particles is disposed on an upper surface and/or a lowersurface of the light diffusion plate, and the concentration of scatteredparticles in the scattered particle layer disposed on the thin plateportion is less than the concentration of scattered particles in thescattered particle layer disposed on the thick plate portion, a similareffect can be obtained.

What is claimed is:
 1. A planar light source comprising: a mountingsubstrate; a plurality of light sources arranged two-dimensionally onthe mounting substrate in a plan view; a partition member including awall portion surrounding each of the light sources except for outermostones of the light sources in the plan view, and wall portions beinglocated inward of the outermost ones of the light sources; a frame bodyhaving a bottom portion and a lateral wall surrounding the mountingsubstrate; a wavelength conversion member disposed on the lateral wallof the frame body; and a light diffusion plate disposed above theplurality of light sources and the wavelength conversion member.
 2. Theplanar light source according to claim 1, wherein a distance between anoutermost light source among the plurality of light sources and thelateral wall is greater than a distance between the outermost lightsource and a top portion of a corresponding wall portion of thepartition member.
 3. The planar light source according to claim 1,wherein a top end of the wavelength conversion member is located lowerthan or at a same height as a top end of the partition member withrespect to the mounting substrate.
 4. The planar light source accordingto claim 1, wherein the partition member includes a bottom portionconnected to a lower end of the wall portion located between the lightsources.
 5. The planar light source according to claim 4, wherein thepartition member further includes a bottom portion located outward ofthe outermost light source.
 6. The planar light source according toclaim 1, wherein the lateral wall of the frame body is perpendicular toan upper surface of the mounting substrate.
 7. The planar light sourceaccording to claim 1, wherein the light diffusion plate has a thicknessthat is thinner in a region between the outermost light source and thelateral wall than in other regions.
 8. A planar light source comprising:a mounting substrate; a plurality of light sources arrangedtwo-dimensionally on the mounting substrate in a plan view; a frame bodyhaving a bottom portion and a lateral wall surrounding the mountingsubstrate; a wavelength conversion member disposed on the lateral wallof the frame body, wherein a distance between the wavelength conversionmember and an outermost light source among the plurality of lightsources is greater than a distance between two light sources among theplurality of light sources; and a light diffusion plate disposed abovethe plurality of light sources and the wavelength conversion member. 9.The planar light source according to claim 8, wherein the lateral wallof the frame body is perpendicular to an upper surface of the mountingsubstrate.
 10. The planar light source according to claim 8, wherein thelight diffusion plate has a thickness that is thinner in a regionbetween the outermost light source and the lateral wall than in otherregions.